Atomic layer deposited conductive tungsten coating enabling ultrahigh-rate capability for commercial LiFePO4 cathodes

Abstract

Due to the high electron diffusion barrier, electron transport is challenging in lithium iron phosphate (LFP) materials. Commercial LFP cathodes typically rely on carbon coating to achieve moderate rate capability (e.g., 70% capacity retention at 5 C). However, this carbon coating often suffers from insufficient uniformity, limiting cathodes’ high-rate performance. In this study, a conformal tungsten (W) coating is applied to commercial LFP particles using atomic layer deposition (ALD) technique. The surface modified cathode material (2W@LFP) exhibits a significant (224%) increase in electrical conductivity, as confirmed by conductive atomic force microscopy and four-point probe measurements. High-scan-rate cyclic voltammetry and COMSOL simulation reveal that the metallic W coating help maintain capacity at high rates by enabling rapid charge transfer through the fast intercalation/deintercalation of lithium ions in the near-surface region of the LFP particles. Exceptional high-rate performance is achieved with the 2W@LFP, delivering a capacity of 113.5 mAh/g at 30 C. In pouch cells, it also exhibits a capacity retention of 76% at a 30 C charge-discharge rate, in sharp contrast to that of the commercial LFP cathodes (which exhibits merely 1% capacity retention at 5 C). X-ray photoelectron spectroscopy analysis reveals that the W coating also effectively mitigates HF corrosion. This work demonstrates that ALD W coating is a highly effective strategy for developing next-generation high-power LFP batteries.